In the current GSM requirements for measurement reporting in 3GPP TS 45.008, titled “3rd Generation Partnership Project; Technical Specification Group GSM/Edge Radio Access Network; Radio subsystem link control (Release 9), 2009-11, (hereinafter 3GPP TS 45.008), the network may configure and/or request that the user equipment (e.g., a mobile station) during an active connection (e.g., a voice call or a packet data transfer) report the serving cell and the neighboring cell measurements via measurements reports and/or enhanced measurement reports. These measurements enable the network to decide whether the user equipment should be directed to another neighboring cell by means of e.g. handover, cell change order, etc. For example, the user equipment may measure the signal level and/or signal quality of the serving GSM cell (e.g., the signal level of the received broadcast control channel carried by the downlink of the base station of the serving cell), and measure the signal level and/or signal quality of a neighboring cell (e.g., the signal level of the received broadcast control channel carried by the downlink of the base station of the neighboring cell).
The reported measurements allow the network to determine whether a handover or a cell change order should be initiated from the serving cell to the neighboring cell.
When reporting the measurements of neighboring cells, the user equipment may be required to report, in addition to measurements of GSM cells, one or more measurements of neighboring inter-RAT cells, e.g., neighboring cells of other radio access technologies, such as UTRAN or E-UTRAN. Due to the limited space in the messages for measurement reporting, there may not be sufficient space to report measurements for all of the valid inter-RAT neighboring cells to the network. As a consequence, 3GPP TS 45.008 at sub clause 8.4.8.1 (which relates to enhanced measurement reporting) states “the cells shall be reported that have the highest sum of the reported value (RXLEV or as defined in sub clause 8.1.5) and the parameter XXX_REPORTING_OFFSET for respective radio access technology/mode.” Given the case of the user equipment supporting more than one RAT and a reporting message with insufficient space to report all valid cells, the user equipment sums the measured (and/or reported) value of received signal level or signal quality, and an offset parameter, XXX_REPORTING_OFFSET, for each of the valid cells of the different RATs, such as UTRAN and E-UTRAN cells. Next, the user equipment compares the sums for each of the RATs. The measurements for the cell(s) with the highest calculated sum among the RATs are then reported. However, a comparison of the calculated sums may not be meaningful as the levels for different RATs (e.g., received signal code power (RSCP) for UTRAN and received signal reference power (RSRP) for E-UTRAN, and the like) may not lend themselves to a direct comparison.
For example, a typical measurement report message from the user equipment to the network may only include 6 positions minus some positions for reporting the measurements of the serving RAT. In that case, the user equipment may have a quantity, N, of valid neighboring UTRAN cells to be reported (e.g., using enhanced reporting) to the network, and a quantity, M, of valid neighboring E-UTRAN cells to be reported to the network. But the measurement report message which is sent from the user equipment to the network may have fewer available positions than the quantity of N+M. Although the network can set an upper limit to the values of N and M by means of parameters XXX_MULTIRAT_REPORTING signaled by the network to the user equipment, this may not always prevent the events described above from occurring. When that is the case, 3GPP TS 45.008 requires that the user equipment reports the neighboring cell(s) according to the highest sum approach noted above and described in TS 45.008 sub clause 8.4.8.1.
Another case where similar measurement reporting issues may occur is in TS 45.008, sub clause 8.4.7 (which relates to normal measurement reporting rather than the enhanced measurement reporting of sub clause 8.4.8), stating: “If there are still remaining positions, these shall be used to report the next best valid cells in other radio access technologies for which XXX_MULTIRAT_REPORTING is non-zero. The best cell is the cell with the highest reported value (see sub clause 8.1.5).” Even in the example of sub clause 8.4.7, the user equipment would need to prioritize between cells of different RATs to decide which cells should be reported to the network in the available spaces of the measurement report message, assuming that the number of cells to be reported is higher than the number of available positions in the measurement report message.
There is also the case where values for the measurement report are different types of values. For example, the value of a RAT may be a signal level, such as RSCP for U IRAN or RSRP for E-UTRAN, and for another RAT may be signal quality, such as Ec/N0 (i.e., energy per chip divided by the power spectral density of the interfering noise) for UTRAN or reference signal received quality (RSRQ) for E-UTRAN. In this example, the user equipment may be required to compare the Ec/N0 value for UTRAN and RSRP value for E-UTRAN and then decide which cell has the highest sum (possibly with the addition of the corresponding XXX_REPORTING_OFFSET) for inclusion in the measurement report. This example illustrates that comparisons of such different types of values may comply with TS 45.008 sub clauses 8.4.7 and 8.4.8.1 but not provide a meaningful comparison to determine which neighboring cells should be reported to the network.